1. FIELD OF THE INVENTION
The present invention relates to a connector for forming a stack of circuit boards each one of which has an array of plated through holes therein and, in particular, to a connector for that purpose using a contact that is itself provided with an expansible barrel having a reflowable solderable material over a portion of at least the interior surface thereof.
2. DESCRIPTION OF THE PRIOR ART
It is often necessary during the manufacture of electrical apparatus to stack plural electrical circuit boards in order to achieve a desired board packaging density and/or to enhance system speed. A typical environment in which this need arises is the so-called high speed super computer. Other areas in which the need for stacked plural boards arises include personal computers, small and mid-size mainframe computers, and other computing apparatus having the need for dense packaging format.
Each of the boards has integrated circuits or discrete passive components mounted thereon. The components are connected by conductive traces formed on the board's surface. The tracings typically terminate in plated through holes. Such through holes are bores through the thickness dimension of the board that are typically lined with copper overplated with tin/lead.
An arrangement which may be used to effect the stacked interconnection of any predetermined number of boards uses a "hermaphroditic" contact. This contact is shown on pages 2 and 3 of Du Pont Connector System Ribcage Bulletin 2800 (December 1984). The hermaphroditic contact is so named because the inclusion of both a male pin and a female receptacle in the same element gives it the ability to mate with another element of the same kind. To effect a stack using hermaphroditic contacts the pin portion of the contact is inserted from a first surface of the board through the plated through hole in a board so that it extends from the opposite surface of the board. The pin is hand soldered in place. The receptacle portion of the contact projects upwardly above the first surface of the board. The pins soldered into a given board may engage into the receptacles of another board also provided with hermaphroditic contacts. The receptacles of the given board may receive the pins of yet a third board similarly provided with hermaphroditic contacts. Such an arrangement of three boards B-1, B-2 and B-3, each having plated through holes H therein, is illustrated in side section in FIG. 10. The contacts are indicated by the reference character C. In a similar manner any number of boards may be stacked by simply inserting the pins from one of two vertically adjacent boards into the receptacles on the other of the vertically adjacent boards.
The use of hermaphroditic contacts to form stacks of boards has readily identifiable disadvantages associated therewith. Prominent among the disadvantages is the time required to effect a hand-soldered interconnection between each individual pin and its associated plated through hole. When one considers that thousands of such solder joints may be required in a given installation it is quickly realized that a serious drawback in manufacturing cost attends the use of hand soldered hermaphroditic contacts to form stacked boards. In addition the reliability of the hand soldered joints is open to question.
Accordingly, in view of the foregoing it is believed to be advantageous to provide a connector whereby a stacked plurality of two or more boards having plated through holes therein may be effected that avoids the drawbacks of the presently available system.